REY’s verifier is a proxy to REY apps that is an important part of REY’s architecture.

Detailed information about it can be found at REY’s tech paper. In essence, the verifier acts as a proxy to certify that the data transference between client and app conforms to a schema that has been accepted by the subject when signing the read permission. Thus, the verifier prevents data leaks in the system while being unable to view the actual data, which is transmitted in an encrypted way from REY apps to clients.

From the development point of view, a verifier needs to be running so that apps are queried through it by clients.